1. Field of the Invention
The present invention relates to a driving mechanism of a wrist of a robot, and in particular to a technique for securing a sufficient space for arranging cables/pipes for supplying energy and/or fluid to a tool to be attached to an end of the wrist without complication of structure of the driving mechanism.
2. Description of Related Art
There is known a wrist driving mechanism having three degrees of freedom around three axes and a space for arranging cables/popes in a robot arm, as disclosed in JP 2000-334689A and EP 0873826B1. In the prior art, hollow drive shafts having different diameters for the three axes are concentrically arranged along an axis of rotation of the robot arm for providing the space for arranging the cables/pipes in the inner hollow shaft.
In the above structure, in order to arranging a large number of cables/pipes in the space in the inner hollow drive shaft, it is necessary to design diameters of the drive shafts for the three axes larger to secure a sufficient space in the inner shaft. However, if the diameters of the drive shafts are made larger, a diameter of the robot arm is made greater to increase a possibility of causing an interference between the robot arm and a peripheral device in an operation of the robot. Further, weight of the robot arm increases to lower controllability of the robot.